1. Field of the Invention
The present invention relates to a process for producing a unit from two plastic parts. More specifically, the present invention relates to a process especially applicable for producing small plastic housings used in various applications including small plastic housings for electrical equipment used in motor vehicle construction.
2. Description of Related Art
Processes for producing a unit from two plastic parts, such as a small plastic housing, are known in the art. In the prior art, two plastic parts are produced separately in a molding production process. Each part is provided with a connection region and generally includes at least one elastically resilient snap-in connector which is formed on the two plastic parts. When the two plastic parts are aligned in an position, these snap-in connectors are also aligned so that the aligned connectors may be locked together. There may be a plurality of these snap-in connectors at several locations on the two plastic parts. Thus, when the two plastic parts are aligned and the snap-in connectors of the two parts are locked together, the two plastic parts are also joined together to form the unit.
These "snap-in" designs, however, have material selection limitations if a tight and secure interface between the two plastic parts are required in the unit such that there is no movement or "play" between the plastic parts. If considerable overextension of the snap-in connectors occurs when the plastic parts are locked together, the plastic material selected must have sufficient pre-stressing force to ensure the tightness of the connection of the two plastic parts when the locking position of the snap-in connectors is reached. Therefore, this force requirement limits the type of plastic composition that can be used and special care must be exercised in the selection of the composition of the plastic. Although plastics which have such sufficient pre-stressing force are difficult and costly to design, because the snap-in connection is simple and can be readily manufactured by using uncomplicated molding machines, this process is commonly used in industry to produce units from two plastic parts.
Another process for producing a unit from two plastic parts is known in the area of the production of collapsible shipping boxes as is disclosed in published German Patent Application DE-A-27 33 964. This reference discloses shipping boxes made from two plastic pieces with connection recesses that are situated next to one another when the parts are placed in an position. A hinge pin is inserted in the connection recesses thereby forming a shipping box from the two plastic parts. This production technique, however, results in two plastic pieces being hingeably joined together and does not result in a unit where the plastic parts are joined together tightly, securely and without play. Therefore, there is an unfulfilled need for a process for producing a unit, such as a housing from two plastic parts, where the two plastic parts are held together in a tight and secure interface without movement or "play" between the two parts.